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console: Move userspace I/O out of console_lock to fix lockdep warning 

When running certain workload on a debug kernel with lockdep turned on,
a ppc64 kvm guest could sometimes hit the following lockdep warning:

  [ INFO: possible circular locking dependency detected ]
  Possible unsafe locking scenario:

        CPU0                    CPU1
        ----                    ----
   lock(&mm->mmap_sem);
                                lock(console_lock);
                                lock(&mm->mmap_sem);
   lock(cpu_hotplug.lock);

  *** DEADLOCK ***

Looking at the console code, the console_lock-->mmap_sem scenario will
only happen when reading or writing the console unicode map leading to
a page fault.

To break this circular locking dependency, all the userspace I/O
operations in consolemap.c are now moved outside of the console_lock
critical sections so that the mmap_sem won't be acquired when holding
the console_lock.

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Waiman Long 2016-11-23 14:06:45 -05:00 committed by Greg Kroah-Hartman
parent 5020ded783
commit 7edd7e82b9
1 changed files with 74 additions and 41 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

115
drivers/tty/vt/consolemap.c
View File

@ -9,6 +9,17 @@
* Support for multiple unimaps by Jakub Jelinek <jj@ultra.linux.cz>, July 1998
*
* Fix bug in inverse translation. Stanislav Voronyi <stas@cnti.uanet.kharkov.ua>, Dec 1998
*
* In order to prevent the following circular lock dependency:
* &mm->mmap_sem --> cpu_hotplug.lock --> console_lock --> &mm->mmap_sem
*
* We cannot allow page fault to happen while holding the console_lock.
* Therefore, all the userspace copy operations have to be done outside
* the console_lock critical sections.
*
* As all the affected functions are all called directly from vt_ioctl(), we
* can allocate some small buffers directly on stack without worrying about
* stack overflow.
*/
#include <linux/module.h>
@ -22,6 +33,7 @@
#include <linux/console.h>
#include <linux/consolemap.h>
#include <linux/vt_kern.h>
#include <linux/string.h>
static unsigned short translations[][256] = {
/* 8-bit Latin-1 mapped to Unicode -- trivial mapping */
@ -309,18 +321,19 @@ static void update_user_maps(void)
int con_set_trans_old(unsigned char __user * arg)
{
int i;
unsigned short *p = translations[USER_MAP];
unsigned short inbuf[E_TABSZ];
if (!access_ok(VERIFY_READ, arg, E_TABSZ))
return -EFAULT;
console_lock();
for (i=0; i<E_TABSZ ; i++) {
for (i = 0; i < E_TABSZ ; i++) {
unsigned char uc;
__get_user(uc, arg+i);
p[i] = UNI_DIRECT_BASE | uc;
inbuf[i] = UNI_DIRECT_BASE | uc;
}
console_lock();
memcpy(translations[USER_MAP], inbuf, sizeof(inbuf));
update_user_maps();
console_unlock();
return 0;
@ -330,35 +343,37 @@ int con_get_trans_old(unsigned char __user * arg)
{
int i, ch;
unsigned short *p = translations[USER_MAP];
unsigned char outbuf[E_TABSZ];
if (!access_ok(VERIFY_WRITE, arg, E_TABSZ))
return -EFAULT;
console_lock();
for (i=0; i<E_TABSZ ; i++)
for (i = 0; i < E_TABSZ ; i++)
{
ch = conv_uni_to_pc(vc_cons[fg_console].d, p[i]);
__put_user((ch & ~0xff) ? 0 : ch, arg+i);
outbuf[i] = (ch & ~0xff) ? 0 : ch;
}
console_unlock();
for (i = 0; i < E_TABSZ ; i++)
__put_user(outbuf[i], arg+i);
return 0;
}
int con_set_trans_new(ushort __user * arg)
{
int i;
unsigned short *p = translations[USER_MAP];
unsigned short inbuf[E_TABSZ];
if (!access_ok(VERIFY_READ, arg, E_TABSZ*sizeof(unsigned short)))
return -EFAULT;
console_lock();
for (i=0; i<E_TABSZ ; i++) {
unsigned short us;
__get_user(us, arg+i);
p[i] = us;
}
for (i = 0; i < E_TABSZ ; i++)
__get_user(inbuf[i], arg+i);
console_lock();
memcpy(translations[USER_MAP], inbuf, sizeof(inbuf));
update_user_maps();
console_unlock();
return 0;
@ -367,16 +382,17 @@ int con_set_trans_new(ushort __user * arg)
int con_get_trans_new(ushort __user * arg)
{
int i;
unsigned short *p = translations[USER_MAP];
unsigned short outbuf[E_TABSZ];
if (!access_ok(VERIFY_WRITE, arg, E_TABSZ*sizeof(unsigned short)))
return -EFAULT;
console_lock();
for (i=0; i<E_TABSZ ; i++)
__put_user(p[i], arg+i);
memcpy(outbuf, translations[USER_MAP], sizeof(outbuf));
console_unlock();
for (i = 0; i < E_TABSZ ; i++)
__put_user(outbuf[i], arg+i);
return 0;
}
@ -536,10 +552,20 @@ int con_set_unimap(struct vc_data *vc, ushort ct, struct unipair __user *list)
{
int err = 0, err1, i;
struct uni_pagedir *p, *q;
struct unipair *unilist, *plist;
if (!ct)
return 0;
unilist = kmalloc_array(ct, sizeof(struct unipair), GFP_KERNEL);
if (!unilist)
return -ENOMEM;
for (i = ct, plist = unilist; i; i--, plist++, list++) {
__get_user(plist->unicode, &list->unicode);
__get_user(plist->fontpos, &list->fontpos);
}
console_lock();
/* Save original vc_unipagdir_loc in case we allocate a new one */
@ -557,8 +583,8 @@ int con_set_unimap(struct vc_data *vc, ushort ct, struct unipair __user *list)
err1 = con_do_clear_unimap(vc);
if (err1) {
console_unlock();
return err1;
err = err1;
goto out_unlock;
}
/*
@ -592,8 +618,8 @@ int con_set_unimap(struct vc_data *vc, ushort ct, struct unipair __user *list)
*vc->vc_uni_pagedir_loc = p;
con_release_unimap(q);
kfree(q);
console_unlock();
return err1;
err = err1;
goto out_unlock;
}
}
} else {
@ -617,22 +643,17 @@ int con_set_unimap(struct vc_data *vc, ushort ct, struct unipair __user *list)
/*
* Insert user specified unicode pairs into new table.
*/
while (ct--) {
unsigned short unicode, fontpos;
__get_user(unicode, &list->unicode);
__get_user(fontpos, &list->fontpos);
if ((err1 = con_insert_unipair(p, unicode,fontpos)) != 0)
for (plist = unilist; ct; ct--, plist++) {
err1 = con_insert_unipair(p, plist->unicode, plist->fontpos);
if (err1)
err = err1;
list++;
}
/*
* Merge with fontmaps of any other virtual consoles.
*/
if (con_unify_unimap(vc, p)) {
console_unlock();
return err;
}
if (con_unify_unimap(vc, p))
goto out_unlock;
for (i = 0; i <= 3; i++)
set_inverse_transl(vc, p, i); /* Update inverse translations */
@ -640,6 +661,7 @@ int con_set_unimap(struct vc_data *vc, ushort ct, struct unipair __user *list)
out_unlock:
console_unlock();
kfree(unilist);
return err;
}
@ -735,9 +757,15 @@ EXPORT_SYMBOL(con_copy_unimap);
*/
int con_get_unimap(struct vc_data *vc, ushort ct, ushort __user *uct, struct unipair __user *list)
{
int i, j, k, ect;
int i, j, k;
ushort ect;
u16 **p1, *p2;
struct uni_pagedir *p;
struct unipair *unilist, *plist;
unilist = kmalloc_array(ct, sizeof(struct unipair), GFP_KERNEL);
if (!unilist)
return -ENOMEM;
console_lock();
@ -750,21 +778,26 @@ int con_get_unimap(struct vc_data *vc, ushort ct, ushort __user *uct, struct uni
for (j = 0; j < 32; j++) {
p2 = *(p1++);
if (p2)
for (k = 0; k < 64; k++) {
if (*p2 < MAX_GLYPH && ect++ < ct) {
__put_user((u_short)((i<<11)+(j<<6)+k),
&list->unicode);
__put_user((u_short) *p2,
&list->fontpos);
list++;
for (k = 0; k < 64; k++, p2++) {
if (*p2 >= MAX_GLYPH)
continue;
if (ect < ct) {
unilist[ect].unicode =
(i<<11)+(j<<6)+k;
unilist[ect].fontpos = *p2;
}
p2++;
ect++;
}
}
}
}
__put_user(ect, uct);
console_unlock();
for (i = min(ect, ct), plist = unilist; i; i--, list++, plist++) {
__put_user(plist->unicode, &list->unicode);
__put_user(plist->fontpos, &list->fontpos);
}
__put_user(ect, uct);
kfree(unilist);
return ((ect <= ct) ? 0 : -ENOMEM);
}